Chemical information, definition

Carhart R E, D H Smith and R Venkataraghavan 1985. Atom Pairs as Molecular Features in Structure Activity Studies Definition and Applications. Journal of Chemical Information and Computer Scienc 25 64-73. 

CRS provides information on chemical substances and how they are represented in the Environmental Protection Agency regulations and data systems. A search engine for chemicals by CAS number, name, molecular formula, chemical type, definition, or other data identifiers. 

Current chemical information systems offer three principal types of search facility. Structure search involves the search of a file of compounds for the presence or absence of a specified query compound, for example, to retrieve physicochemical data associated with a particular substance. Substructure search involves the search of a file of compounds for all molecules containing some specified query substructure of interest. Finally, similarity search involves the search of a file of compounds for those molecules that are most similar to an input query molecule, using some quantitative definition of structural similarity. 

In order to achieve selective complexation and to perform specific functions, chemical information has to be stored in L and read out by S. Information storage may be accomplished in the design of the ligand system and readout is contained in the dynamics of the complexation process. These various definitions are interrelated in the flow chart given in Figure 1. 

In 1997, D.L. Massart suggested the following definition "Chemometrics is a chemical discipline that uses mathematics, statistics and formal logic (a) to design or select optimal experimental procedures (b) to provide maximum relevant chemical information by analyzing chemical data and (c) to obtain knowledge about chemical systems" (Massart et ah, 1997). 

It should be remembered that few in Porta s time were free from credulity toward many marvels and superstitions which were inherited from the past and Porta s work shows that he was no exception, as much of the marvellous is found in his writings. On the whole, however, his information is definite and practical and his work is as good as could be expected of one not himself a practical experimenter or investigator, but a conscientious and scholarly student of the literature, ancient and contemporary. His directions and recipes on a great variety of applications of chemistry are sufficiently definite and detailed to be of service in stimulating experimentation and all in all, the work must have been of considerable influence in disseminating interesting and useful chemical information. 

Chapter 9, Investigation and Characterisation of Organic Compounds, contains much of the chemical information and preparative methods from the chapter previously entitled Qualitative Analysis. The emphasis of this chapter is now on achieving an understanding of chemical behaviour in association with spectroscopic features, and correlating this information to provide a definitive structural elucidation. In this way we hope that the material fulfils the requirements of a range of courses which deal in this topic. The tables of physical constants (Ch. 10) remain unchanged, and the appendices have been up-dated.. ... 

This definition is important because it means that an unexpected product such as the result of a rearrangement is treated as an exception in the same way as products arising from impurities etc. From a chemical information perspective, this means that a library is defined by one or more transformations from reagents to R-groups and the way in which the R-groups are joined together. 

Chemical sensors are by definition small, inexpensive and preferably hand-held devices, capable of continuously monitoring chemical constituents in liquids or gases. MIP sensors usually consist of an imprinted sensitive layer and a transducer to convert the chemical information, in real time, into an electrical or optical signal which is further evaluated electronically [12]. Figure 21.1 shows the set-up of chemosensors and two typical mass-sensitive devices. 

Note that this Principle is simply a restatement of the experimental evidence which led to Table 1.2. It is a condensed statement of a very large amount of chemical information. As such it might be called a law. But this label seems pretentious in view of the lack of a quantitative definition of hardness. HSAB is not a theory, since it does not explain variations in the strength of chemical bonds. The word prefer in the HSAB Principle implies a rather modest effect. Softness is not the only factor which determines the values of A/Z° in Equation (1.1). There are many examples of very strong bonds between mismatched pairs, such as H2, formed from hard H+ and soft H. H2O, OH and 0 are all classified as hard bases, but there are great differences in their base strength, by any criterion. 

In this part of the book, fundamental chemical information of interest to petroleum chemists is given. The first chapter deals with the main definitions as well as the important properties of crude oil and petroleum products used by petroleum specialists. A short history is given as to how crude oil became the most important power source for our civilization for over thousands of years. 

These experimental electron density distributions are in accord with the VB, MO, and DFT descriptions of chemical bonding, but are not easily applied to the determination of the relatively small differences caused by substituent effects that are of primary interest in interpreting reactivity. As a result, most efforts to describe electron density distribution rely on theoretical computations. The various computational approaches to molecular structure should all arrive at the same correct total electron distribution, although it might be partitioned among orbitals differently. The issue we discuss in this section is how to interpret information about electron density in a way that is chemically informative, which includes efforts to partition the total electron density among atoms. These efforts require a definition (model) of the atoms, since there is no inherent property of molecules that partitions the total electron density among individual atoms. 

First of all, what is Chemometrics According to the definition of the Chemometrics Society, it is the chemical discipline that uses mathematical and statistical methods to design or select optimal procedures and experiments, and to provide maximum chemical information by analyzing chemical data. ... 

It was shown in Chapter 1 that the Mossbauer effect produced monochromatic y-radiation with a definition of the order of 1 part in 10 and we now seek ways to use this extremely high precision to obtain chemical information. The key to the problem lies in the total interaction Hamiltonian for the atom, which contains terms relating to interactions between the nucleus on the one hand and the electrons (and hence the chemical environment) on the other. The Hamiltonian can be written as... 

In par allel with these approaches, the power of computational predictive methodologies has now reached the stage where a thud strategy, chemical space definition , can be applied to the discovery portfolio to aid in finding pharmaceutical interventions. Information-... 

The definition of P as 2R ensures that these numbers all lie between zero and two and therefore satisfy the obvious simplest requirement of occupation numbers. Since the charge on the electron is the magnitude of the unit of charge we use, these numbers are frequently called the charges associated with each basis function. Chemical information can be obtained now by comparing the Pn (which are the occupation numbers of the AOs within the molecule) with the occupation numbers (i/j) of the same AOs in the separate atoms of which the molecule is composed. 

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